JP4797065B2 - Audio signal processing apparatus and surround signal generation method, etc. - Google Patents

Description

  The present application relates to audio signal processing, and more particularly to the field of technology for generating a surround signal having reflected sound and reverberant sound.

  2. Description of the Related Art Conventionally, SFC (Surround Field Control) technology for simulating a realistic sound field image by adding reflected sound and reverberation sound (reverb) to audio signals such as music and movies is known.

As an example of such a technique, in the surround circuit disclosed in Patent Document 1 (see FIG. 1), the surround signals LS and RS are calculated from the left and right (left channel (Lch) and right channel (Rch)) audio input signals. The surround signals LS and RS are attenuated by the attenuation circuit and then added to the left and right audio input signals by the adder circuit and output. Thereby, a sound having a surround effect is generated for the listener.
JP 2000-102100 A

  However, in such a conventional SFC technique, the surround signal is generated based on the audio input signal (that is, depending on the signal level of the audio input signal). The signal level fluctuates greatly, making it difficult to stabilize the signal level of the output signal. As a result, it is difficult to obtain a natural feeling of sound expansion.

  Accordingly, the present application provides an audio signal processing apparatus, a surround signal generation method, and the like that can obtain a stable output signal level and a sense of breadth that do not depend on an audio input signal, with solving such a problem as one problem. For the purpose.

  In order to solve the above-described problem, according to one aspect of the present application, there is provided an audio input signal input means for inputting an audio input signal corresponding to each of a plurality of channels, and a surround signal having reflected sound or reverberation sound, Surround signal generation means for generating a surround signal corresponding to each of the channels, and the surround signal generation means includes an audio input signal corresponding to one channel and the predetermined time before the corresponding one channel. A surround signal corresponding to the one channel is generated based on a variable that changes within a predetermined range according to the signal level of the surround signal and the audio input signal corresponding to another channel.

  In another aspect of the present application, a step of inputting an audio input signal corresponding to each of a plurality of channels and a surround signal having reflected sound or reverberation sound and corresponding to each of the plurality of channels are generated. A surround signal generating step, wherein the surround signal generating step is within a predetermined range in accordance with an audio input signal corresponding to one channel and a signal level of the surround signal corresponding to the one channel before a predetermined time. A surround signal corresponding to the one channel is generated on the basis of the variable that changes in the above and the audio input signal corresponding to another channel.

  In still another aspect of the present application, an audio input signal input means for inputting an audio input signal corresponding to each of a plurality of channels, a surround signal having reflected sound and reverberation sound, and a computer for each of the plurality of channels. The surround signal generation means is configured to function as a surround signal generation means for generating a corresponding surround signal, and the surround signal generation means includes an audio input signal corresponding to one channel and a signal level of the surround signal before a predetermined time corresponding to the one channel. A surround signal corresponding to the one channel is generated based on a variable that changes within a predetermined range in accordance with the audio input signal corresponding to another channel.

  In still another aspect of the present application, the surround signal generation processing program is stored in a computer-readable manner.

It is a figure which shows the example of a schematic structure of the audio reproduction apparatus which concerns on this embodiment. It is a figure which shows the production | generation signal flow of the audio output signals Lo and Ro in DSP5. It is a figure which shows the detail of the production | generation signal flow of the surround signal Ls in the surround signal production | generation part shown in FIG. (A) is a figure which shows an example of a motion of "cos ((theta) 1-theta2 | Ls |)" when (theta) 1 = (pi) and (theta) 2 = (pi) / 4, (B) is the figure which shows (theta) 1 = 2 (pi) / 3. It is a figure which shows an example of a motion of "cos ((theta) 1- (theta) 2-Ls |)" when it is set to (theta) 2 =-(pi) / 6. It is a figure which shows the modification of the production | generation signal flow of the audio output signals Lo and Ro shown in FIG.

Explanation of symbols

1 Disc playback unit 2 Tuner 3 A / D converter 4 Source switching unit 5 DSP
6a, 6b D / A converter 7a, 7b Amplifier 8a, 8b Speaker 9 System control unit 10 Operation / display unit 41 Surround signal generation unit S Audio playback device

  Hereinafter, the best embodiment of the present application will be described with reference to the drawings. In addition, embodiment described below is embodiment at the time of applying this application with respect to the audio reproducing apparatus installed in the vehicle interior or the interior of a building.

  First, the configuration and function of the audio playback apparatus according to the present embodiment will be described with reference to FIG.

  FIG. 1 is a diagram illustrating a schematic configuration example of an audio playback device according to the present embodiment.

  As shown in FIG. 1, an audio playback device S is a disc that reads recorded information from a disc such as an MD (Mini Disc), a CD (Compact Disc), or a DVD (Digital Versatile Disc), and plays back and outputs audio input signals L and R. The reproduction unit 1, a tuner 2 that receives broadcast waves broadcast from a television broadcast or radio broadcast, reproduces and outputs the audio input signals Li and Ri, and analog / digital converts the audio input signals Li and Ri from the tuner 2. A / D converter 3 for output, source switching unit 4 for switching and outputting audio input signals Li and Ri from disc playback unit 1 and audio input signals Li and Ri from A / D converter 3, and source switching A DSP (Digital Signal Processor) 5 that performs signal processing to be described later on the audio input signals Li and Ri from the unit 4 and outputs audio output signals Lo and Ro; D / A converters (DACs) 6a and 6b that output the audio output signals Lo and Ro from SP5 by digital / analog conversion, and audio output signals Lo and Ro from the D / A converters 6a and 6b are amplified. Amplifiers 7a and 7b that output, speakers 8a and 8b that output audio output signals Lo and Ro from the amplifiers 7a and 7b as sound waves, a system control unit 9, operation buttons that receive various operation instructions from the user, and various types And an operation / display unit 10 having a display panel for displaying information.

  Since the functions of the disc playback unit 1 and the tuner 2 are known, detailed description thereof is omitted.

  Here, the audio input signal Li corresponds to the left channel (hereinafter referred to as “Lch”), the audio input signal Ri corresponds to the right channel (hereinafter referred to as “Rch”), and the audio input signal Li and audio The input signal Ri is a stereo signal with different sound sources recorded from each other.

  The system control unit 9 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a working RAM (Random Access Memory), and the like. The CPU executes a predetermined program, and an instruction (for example, for example) The audio playback instruction, tuning instruction, source switching instruction, etc.) are controlled according to the signal.

  The DSP 5 functions as an audio input signal input unit, a surround signal generation unit, and an audio output signal generation unit of the present application by executing predetermined programs including the surround signal generation processing program of the present application. The audio input signals Li and Ri corresponding to each of the audio signals are input, and the surround signals Ls and Rs corresponding to the Lch and Rch, respectively, which are reflected sound and reverberation sound are generated, and the above audio is provided for each channel. The input signals Li and Ri and the surround signals Ls and Rs are added to generate audio output signals Lo and Ro (for example, the audio input signal Li and the surround signal Ls corresponding to the channel of the audio input signal Li are added). To generate an audio output signal Lo) and output it respectively.

  Note that the surround signal generation processing program of the present application may be stored in advance in, for example, a ROM or the like provided in the audio playback device S, or may be stored and stored in a predetermined server connected to the Internet or the like, for example. Downloaded from the server to the audio playback device S and stored in, for example, a non-volatile memory or a hard disk provided in the audio playback device S, or the program recorded on a recording medium such as a CD-ROM is recorded via a drive or the like. You may comprise so that the reproducing | regenerating apparatus S may read and memorize | store in a non-volatile memory or a hard disk.

  Further, the DSP 5 may be configured such that the Lch and the Rch are provided separately.

  Next, a basic concept of the surround signal and audio output signal generation method in the DSP 5 will be described.

  The surround signals Ls and Rs are generated based on the following equations (1) and (2).

Ls (t) = Li (t) + Ri (t) cos (θ1−θ2 | Ls (t-1) |) (1)
Rs (t) = Ri (t) + Li (t) cos (θ1−θ2 | Rs (t-1) |) (2)
Here, t indicates time, and | Ls (t-1) | is the signal level of the surround signal Ls (t-1) a predetermined time before the surround signal Ls (t) (for example, one sampling time). Indicates the absolute value of (amplitude: proportional to the volume of the sound), and | Rs (t-1) | is the surround signal Rs () for a predetermined time before the surround signal Rs (t) (for example, one sampling time). The absolute value of the signal level (amplitude) of t-1) is shown. Further, the amplitudes of the surround signals Ls and Rs are adjusted so as to fluctuate in a range of −2 (minimum value) to 2 (maximum value). Θ1 and θ2 can be arbitrarily set according to a desired sound field (for example, when a user operates an operation button).

  Thereby, the surround signal Ls changes within a predetermined range in accordance with the signal level of the audio input signal Li and the surround signal Ls (surround signal corresponding to Lch) before a predetermined time (for example, a time corresponding to one sampling). It can be seen that it is generated based on the variable (cos (θ1−θ2 | Ls |)) and the audio input signal Ri.

  On the other hand, the surround signal Rs changes within a predetermined range in accordance with the signal level of the audio input signal Ri and the surround signal Rs (surround signal corresponding to Rch) before a predetermined time (for example, one sampling time). It can be seen that it is generated based on the variable (cos (θ1−θ2 | Rs |)) and the audio input signal Li.

  In this example, the variable that changes within a predetermined range according to the signal level of the surround signal is a variable obtained by a cosine function (cos θ), and the predetermined range is any value between −1 and +1. It becomes the range.

  As described above, the surround signals Ls and Rs are generated based on the surround signals Ls and Rs of a predetermined time before the range is stabilized by limiting the range by the cosine function (cos θ) (for example, one sample before). (It does not depend only on the audio input signal L).

By the way, "- cos (θ1-θ2│Ls (t -1) │) " was used as a w _L, "- cos (θ1-θ2│Rs (t -1) │) " the When w _R, the above-mentioned (1 ), (2) can be transformed into the following (3), (4), respectively (t is omitted for simplicity).

Ls = Li−Liw _L (3)
Rs = Ri−Liw _R (4)
For example, from equation (3), the surround signal Ls is subtracted from the audio input signal Li component audio input signal Ri components of the other channels by the ratio of w _L (subtracting) obtained by the audio input signal Ri component Is controlled by cos θ (similar idea for the surround signal Rs).

  The audio output signals Lo and Ro are generated based on the following equations (5) and (6).

Lo (t) = Li (t) + Ls (t) (5)
Ro (t) = Ri (t) + Rs (t) (6)
For example, from the above equation (5), it can be seen that the audio output signal Lo is generated by adding the audio input signal Li and the surround signal Ls.

  Next, more specific processing in the DSP 5 will be described with reference to FIGS.

  FIG. 2 is a diagram showing a signal flow for generating the audio output signals Lo and Ro in the DSP 5, which shows a specific signal flow based on the above equations (5) and (6). FIG. 3 is a diagram showing details of a signal flow for generating the surround signal Ls in the surround signal generating unit shown in FIG. 2, and this shows a specific signal flow based on the above equation (1). is there. The signal flow for generating the surround signal Rs is similar to that shown in FIG. 3 except that L and R are reversed. Therefore, the illustration is omitted and the description overlapping the generation of the surround signal Rs is omitted. Also, each part shown in 41 to 43 in FIG. 2 and each part shown in 51 to 59 in FIG. 3 represent a calculation processing part executed by the DSP 5.

  In the generation signal flow of the audio output signals Lo and Ro shown in FIG. 2, the audio input signal Li input to the DSP 5 is input to the surround signal generation unit 41 and the addition unit 42, and the audio input signal Ri is the surround signal generation unit. 41 and the adder 43.

  Next, in the signal flow for generating the surround signal Ls shown in FIG. 3, the adder 51 adds the audio input signal Li and the intermediate signal Rim to generate the surround signal Ls. The surround signal Ls is generated by the branching unit 52. One is output from the surround signal generator 41 and the other is fed back.

  In the process of feeding back the other surround signal Ls, first, the surround signal Ls one time before the sampling is extracted by the previous signal extraction 53.

  Next, the absolute value of the surround signal Ls before one sampling time is calculated by the absolute value calculation unit 54, and then passed through a first-order low-pass filter 55 as an example of a time constant circuit, so that a predetermined time constant is obtained. Accordingly, the rise of the signal is moderated. The reason why the low-pass filter 55 is passed is to suppress a sudden change in the surround signal Ls and make it smooth.

  Next, the absolute value of the surround signal Ls that has passed through the low-pass filter 55 is multiplied by a preset θ 2 by the multiplier 56, and as a result, “θ 2 | Ls |” is calculated.

  Next, θ1 and −θ2 | Ls | set in advance are added by the adder 57, and then cos (θ1−θ2 | Ls |) is calculated by a cos (cosine) calculator 58.

  Next, the calculated cos (θ1−θ2 | Ls |) and the audio input signal Ri are multiplied by the multiplier 59 to generate an intermediate signal Rim (multiplied signal).

  The generated intermediate signal Rim is added to the audio input signal Li by the adder 51 to generate and output a surround signal Ls.

  The surround signal Ls generated and output from the surround signal generation unit 41 is input to the addition unit 42 and added to the audio input signal Li to generate an audio output signal Lo and output from the DSP 5 as shown in FIG. (In actuality, the audio output signal Lo is output after appropriately performing known signal processing such as loudness calculation and EQ in the DSP 5). Similarly, the surround signal Rs output from the surround signal generator 41 is input to the adder 43 and added to the audio input signal Ri to generate an audio output signal Ro and output from the DSP 5 as shown in FIG. Will be.

  When the surround signal Ls and Rs are generated in the surround signal generator 41 with a long time and a delay occurs, the audio input signal and the surround signal are synchronized or the audio input signals Li and Ri and the surround signals Ls and Rs are synchronized. In order to give an arbitrary delay difference to each other, a delay unit is provided in front of the adders 42 and 43, and the audio input signals Li and Ri are transmitted by the delay unit for a predetermined time (a time when synchronization can be established, or an arbitrary delay). It may be configured to input to the adders 42 and 43 after a delay).

  The above processing is performed in time series for each sampling.

  Next, an embodiment in which specific values (desired values) are set for θ1 and θ2 will be described. Note that Lch will be described as a representative.

  FIG. 4A is a diagram illustrating an example of the movement of “cos (θ1−θ2 | Ls |)” when θ1 = π and θ2 = π / 4. When θ1 = π and θ2 = π / 4, as shown in FIG. 4 (A), cos (π−π / 4 | Ls |) depends on the change (0-2) of | Ls | It changes in the range of −1 to 0.

Thus, for example, if the signal level of the surround signal Ls is small, w _L (= −cos (π−π / 4 | Ls |) becomes large (closes to 1). The difference signal component of Li−Ri is dominant in the signal Ls, whereas, for example, when the signal level of the surround signal Ls is large, w _L becomes small (closes to 0), and therefore, from the above equation (3). In the surround signal Ls, the audio input signal Li component is dominant.

In particular, when the audio input signal Li is an audio input signal Ri and the reverse-phase, w _L is large, (sound is small), it is possible to increase the sound approaches the surround signal Ls = Li-Ri = 2Li, w L If is small (sound is loud), it can approach the surround signal Ls = Li and suppress the loud sound. Therefore, it is possible to control so as to stabilize the signal level of the surround signal Ls.

  FIG. 4B is a diagram illustrating an example of the movement of “cos (θ1−θ2 | Ls |)” when θ1 = 2π / 3 and θ2 = −π / 6. When θ1 = 2π / 3 and θ2 = −π / 6, as shown in FIG. 4B, cos (2π / 3 + π / 6 | Ls |) is changed to | Ls | Accordingly, it changes in the range of −0.5 to −1 (that is, changes in a range narrower than that in FIG. 4A).

Thereby, for example, w _L increases as the signal level of the surround signal Ls increases (approaching 0.5 to 1), and therefore the surround signal Ls has a signal level of the above equation (3). Regardless of whether it is large or small, the difference signal component of Li-Ri becomes dominant and the feeling of spreading can be increased, and further, the feeling of spreading can be further increased as the sound becomes louder.

  In addition to the combinations of the values of θ1 and θ2, various combinations are conceivable. As an example, “cos (θ1−θ2 | Ls |)” should be increased or decreased in what range and in what direction (ie, | Ls | changes from 0 to 1). ), It is good to consider the combination of the values of θ1 and θ2. For example, in addition to the combination of the values of θ1 and θ2, it is conceivable that θ1 = 4π / 5 and θ2 = π / 4 are desirable combinations of values.

  It is desirable that the combination of the values of θ1 and θ2 can be selected by the listener by operating the operation / display unit 10.

  For example, in response to a mode selection instruction from the listener via the operation / display unit 10, the system control unit 9 selects a selection button displaying characters of the listening mode 1, the listening mode 2, and the listening mode 3, respectively. When the listening mode 1 is selected and displayed on the display panel of the operation / display unit 10 so as to be selectable, θ1 = π previously stored in association with the mode 1 , Θ2 = π / 4, and when listening mode 2 is selected, θ1 = 2π / 3 and θ2 = −π / 6 stored in advance in association with mode 2 are set. When the listening mode 3 is selected, θ1 = 4π / 5 and θ2 = π / 4 stored in advance in association with the mode 3 are set. Thus, the set values of θ1 and θ2 are transmitted from the system control unit 9 to the DSP 5 and set in the DSP 5. Thereby, the listener can select a desired mode depending on how he / she wants to enjoy audio in the listening space (in other words, a desired sound field).

  As described above, according to the above embodiment, the audio input signals Li and Ri corresponding to the Lch and Rch are input, and the audio input signal Li and the signal level of the surround signal Ls before a predetermined time are input. Based on the variable that changes within the predetermined range and the audio input signal Ri (for example, the audio input signal Ri is multiplied by a variable that changes within the predetermined range according to the signal level of the surround signal Ls before the predetermined time, A surround signal Ls is generated by adding the multiplied signal and the audio input signal Li, and changes within a predetermined range according to the signal level of the audio input signal Ri and the surround signal Rs a predetermined time ago. The surround signal Rs is generated based on the variable and the audio input signal Li, and these surround signals Ls and Rs are input as audio inputs. Since they are added to the signals Li and Ri and output as audio output signals Lo and Ro, a stable output signal level (surround signal and output signal level of the audio output signal) and sound independent of the audio input signals Li and Ri. A feeling of spreading (in other words, a sound effect) can be obtained. For example, when enjoying audio in a vehicle interior, it is possible to improve the sound field impression with a feeling of closure unique to the vehicle interior, and to create a natural sound spread and spatiality.

  In addition, since the variable that changes within a predetermined range according to the signal level of the surround signal is obtained by the cosine function (cos θ), the surround signal can be stabilized by limiting the range more, Since the surround signal is generated by feedback, a more stable surround output signal level and sound spread can be obtained.

  In addition, the value of θ in the cosine function (cos θ) can be arbitrarily set, and the predetermined range is determined by the value of θ, so that an optimal audio output corresponding to the sound field desired by the listener can be obtained. Can be realized.

  In the above embodiment, the generation signal flow of the audio output signals Lo and Ro shown in FIG. 2 is a basic form, and other various arithmetic processing units may be interposed. For example, FIG. 5 is a modification of the signal flow for generating the audio output signals Lo and Ro shown in FIG. 2 (the same components as those in FIG. 2 are given the same reference numerals).

  In the signal flow for generating the audio output signals Lo and Ro shown in FIG. 5, the audio input signals Li and Ri input to the DSP 5 are respectively delayed by delay units 61 and 62 (to synchronize with the surround signal). On the other hand, the surround signals Ls and Rs output from the surround signal generation unit 41 pass through BPFs (band pass filters) 63 and 64, and have a predetermined band (for example, a band in a certain range such as a vocal band). Only the surround signals Ls and Rs are extracted. As a result, it is possible to increase the sense of sound spread only in a predetermined band.

Also, in the generated signal flow shown in FIG. 5, reference numerals 65 to 68 denote addition rate determining units for determining the addition rate between the audio input signal and the surround signal, and the α _L and β _L shown in FIG. The ratio of the audio output signal Lo from the delay unit 61 and the surround signal Ls from the BPF 63 is determined by the ratio, while the audio output from the delay unit 62 is determined by the ratio of α _R and β _R shown in FIG. An addition rate between the signal Ro and the surround signal Rs from the BPF 64 is determined. For example, if α _L : β _L = 1: 0.5, the surround signal Ls whose signal level is attenuated to the original half is added to the audio output signal Lo (by the adder 42), and the audio output signal Lo Will be generated. Thereby, the feeling of sound expansion can be adjusted.

  Further, in the generated signal flow shown in FIG. 5, a delay unit is provided after the BPFs 63 and 64, and the delay unit delays the surround signal Ls from the BPF 63 and the surround signal Ls from the BPF 64 (that is, the audio input signal). (It may be intentionally delayed from Li and Ri). Thereby, it is possible to obtain a feeling of sound expansion different from the above configuration.

  In the above embodiment, the variable that changes within a predetermined range in accordance with the signal level of the surround signal is determined by the cosine function (cos θ). However, the present invention is not limited to this. The sine function (sin θ) may be used. When the sine function (sin θ) is used, the same result can obtain the same effect by shifting (for example, advance) the values of θ 1 and θ 2 by π / 2 with respect to the cosine function (cos θ). it can.

  In the above embodiment, the case of two channels of Lch and Rch has been described as an example. However, in the case of three or more channels, a variable that changes within a predetermined range according to the signal level of the surround signal of one channel The basic configuration of multiplying the audio input signals of other channels and adding the multiplied signals and the audio input signals of one channel to generate a surround signal is the same.

  In the above embodiment, the audio input signals Li and Ri and the surround signals Ls and Rs are added to generate and output the audio output signals Lo and Ro. However, the present invention is not limited to this. The generated surround signals Ls and Rs are output as they are (for example, output from a speaker dedicated to the surround signal (a speaker corresponding to any two channels in the case of 5.1ch)). Also good.

Claims (9)

Audio input signal input means for inputting an audio input signal corresponding to each of a plurality of channels;
Surround signal generating means for generating a surround signal corresponding to each of the plurality of channels, which is a surround signal having reflected sound and reverberant sound;
With
The surround signal generating means includes an audio input signal corresponding to one channel, a variable that changes within a predetermined range according to a signal level of the surround signal corresponding to the one channel before a predetermined time, and another channel An audio signal processing apparatus for generating a surround signal corresponding to the one channel based on the audio input signal corresponding to the first channel. The audio signal processing device according to claim 1,
The surround signal generating means includes
Multiplying the audio input signal corresponding to the other channel by a variable that changes within a predetermined range according to the signal level of the surround signal corresponding to the one channel before the predetermined time, An audio signal processing apparatus that adds the audio input signals corresponding to the one channel to generate a surround signal corresponding to the one channel. The audio signal processing device according to claim 1 or 2,
Audio signal processing further comprising: audio output signal generation means for generating an audio output signal by adding the audio input signal and the surround signal corresponding to the channel of the audio input signal for each channel apparatus. The audio signal processing device according to claim 1,
The audio signal processing apparatus according to claim 1, wherein the variable is obtained by a cosine function or a sine function. The audio signal processing device according to claim 4, wherein
The value of θ in the cosine function or sine function can be arbitrarily set, and the predetermined range is determined by the value of θ. The audio signal processing device according to claim 1,
The surround signal generating means includes
A variable that changes within a predetermined range according to the signal level of the surround signal corresponding to the one channel after passing through the time constant circuit is set to the audio input signal corresponding to the other channel. An audio signal processing apparatus that performs multiplication. Inputting an audio input signal corresponding to each of a plurality of channels;
A surround signal generating step for generating a surround signal having a reflected sound and a reverberant sound and corresponding to each of the plurality of channels;
With
The surround signal generation step includes:
An audio input signal corresponding to one channel, a variable that changes within a predetermined range according to the signal level of the surround signal corresponding to the one channel before a predetermined time, and the audio input signal corresponding to another channel And generating a surround signal corresponding to the one channel. Computer
Audio input signal input means for inputting an audio input signal corresponding to each of a plurality of channels;
It is a surround signal having reflected sound and reverberation sound and functions as a surround signal generating means for generating a surround signal corresponding to each of the plurality of channels,
The surround signal generating means includes
An audio input signal corresponding to one channel, a variable that changes within a predetermined range according to the signal level of the surround signal corresponding to the one channel before a predetermined time, and the audio input signal corresponding to another channel A surround signal generation processing program for generating a surround signal corresponding to the one channel based on the above.   9. A recording medium in which the surround signal generation processing program according to claim 8 is stored so as to be readable by a computer.

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